A new concept in high performance ceria–zirconia oxygen storage capacity material with Al2O3 as a diffusion barrier

Abstract

CeO2–ZrO2 solid solution ((Ce,Zr)O2) is an indispensable oxygen storage capacity (OSC) material for emission control in gasoline-fuelled automobiles. The high performance OSC material developed in this study is composed of Al2O3 as “a diffusion barrier” and (Ce,Zr)O2 particles in intervening layers on a nanometer scale, and is abbreviated as “ACZ”. The Brunauer–Emmett–Teller (BET) specific surface area (SSA) of ACZ after durability testing in air at 1000°C was 20m2/g, which is higher than that of conventional CZ (2m2/g) composed of (Ce,Zr)O2 without Al2O3. After heat treatment at 1000°C in air, the particle size of (Ce,Zr)O2 in ACZ was about 10nm and that without Al2O3 was one-half of the size in pure CZ. The OSC was roughly characterized by the total capacity (OSC-c1) and the oxygen release rate (OSC-r). In a fresh catalyst, ACZ and CZ had almost the same OSC-c1; however, the OSC-r of ACZ was twice as fast as CZ. After durability testing, the OSC-r of both ACZ and CZ were reduced significantly, but the OSC-r of ACZ was about five times as fast as CZ. While the OSC-c1 was hardly influenced by the (Ce,Zr)O2 crystallite size and Pt particle size on the supports, the OSC-r was influenced by both of these parameters. The improvement of the OSC-r in the fresh catalyst and inhibition of the decrease in the OSC-r after durability testing were achieved by suppression of particle growth of (Ce,Zr)O2 in ACZ by introducing Al2O3 as a diffusion barrier with resultant inhibition of sintering of Pt particles.